Measuring and test equipment currently employed by telephone service providers customarily contains a variety of conditioning and signal generation functions which enable service and maintenance personnel to apply a prescribed number of electrical stimuli to a line, such as a (digital) subscriber loop, for the purpose of trouble-shooting the line and measuring its performance. A non-limitative example of such equipment is diagrammatically illustrated in FIG. 1, which shows the distribution of a plurality of (microprocessor-controlled) remote measurement units (RMUs) 11, which are installed at a plurality of sites geographically remote with respect to each other and a supervisory site 12.
An RMU 11 includes various components, such as tone generation and electrical conditioning circuitry which, under the control of a firmware-resident measurement and test mechanism contained in the resident operating system employed by an on-board processor, selectively transmit prescribed test signals to the line, and may also condition the line with electrical circuit parameters, that allow an associated line measurement unit to conduct line measurements and thereby determine the current state of the line and its ability to successfully perform as intended.
For this purpose, each RMU 11 is typically of the type that conforms to computer interface requirements defined in Issue 3 of AT&T Publication KS-23253 and contains internal firmware, which is operative to perform various diagnostic or test operations on network lines 13 and (subscriber) termination equipment 15. The RMU may be accessed by means of one or more video display terminals (VDTs), or data terminal units (DTUs) 21 at the supervisory site 12, which have the capability of accessing the remote test equipments 11 through attendant modem devices 23, such as industry standard Hayes `AT`-compatible 300/1200 units, that are linked to a central office 25.
Because test and conditioning parameters and customer-requested performance features may differ among various pieces of equipment, whenever it is necessary to perform a repair, or effect a change to the functionality of the firmware (e.g. change an instruction set), it is customary practice for a service technician (craftsperson) to travel to the site where the equipment is installed, and either make a component or board replacement in the field, or, as is more often the case, retrieve the unit, bring it back to a servicing site, where a repair or retrofit is performed, and then return the modified unit to the remote site, so that it may be placed back in service.